Engine with hydraulic variable valve timing

ABSTRACT

In one example, a method is described for an engine with a hydraulically actuated phaser for adjusting cam timing. The phaser is controlled by a hydraulic spool valve, for example, having a de-energized position that results in hydraulic force urging the phaser to a base timing. When it is desired to operate the cam timing at base timing, rather then leave the spool valve in a de-energized position that can generate leakage, the spool valve is adjusted to near a null position to reduce the hydraulic pressure drop across the cam journal and thus reduce oil leakage. In this way, it is possible to maintain base timing, while also reducing leakage.

FIELD

The present application relates to methods for operating an engine withvariable cam timing (VCT).

BACKGROUND AND SUMMARY

Internal combustion engines may use variable cam timing (VCT) to improvefuel economy and emissions performance of a vehicle. One method ofvariable cam timing uses an Oil Pressure Actuated device (OPA), such asa vane type cam phaser. The phaser may be controlled by anelectromechanically actuated spool valve that directs oil flow to oneside or the other of the vane. The performance of this device is thusdependent on oil pressure, which can be a function of engine speed andleakage through various oil subsystems. Therefore, the Oil PressureActuated device may have unacceptable performance at low engine speedsor when hydraulic subsystems exhibit high oil leakage.

One example VCT system includes a vane type actuator as well as anoptional biasing spring to hold the cam timing in a base positionwhenever insufficient oil pressure is available to control position ofthe actuator via the spool valve. For example, the base timing may be afully retarded timing desired for engine starting, since sufficient oilpressure is typically unavailable during engine starting operation.

The inventors herein have recognized that OPA cam phasers may beparticularly prone to oil leakage and slow response time when held atbase timing by hydraulic actuation force controlled by the spool valve.Specifically, under this condition, the spool valve is positioned in afull retarding actuation position, as the full retarding actuationposition is often the default (de-energized) state of the spool valve.For the example of a cam-fed oil pressure actuated system, oil leakagemay occur between the advance and retard oil passages in the cam journalbearing due to the pressure differential between the two passages. Inthe base position, oil fully pressurizes the base position oil passagesin the cam journal. Because the oil control valve may have one portfully pressurized and another open to tank (atmosphere) in thede-energized position, too much oil may flow across the small radialclearance and the lateral seal land distance between the two passages inthe cam journal (flow from high to low pressure). Oil flows through theoil passages and out of the drain port in the spool valve may reducemain galley oil pressure and thus create a significant oil pressure dropin the system.

As such, one approach to address the above issues includes a method ofcontrolling an engine, the engine including a hydraulically actuatedvariable cylinder valve actuator coupled to a cylinder valve of theengine. The actuator is controlled by a hydraulic valve adjustable amonga plurality of ranges including a first range generating a hydraulicforce in a first direction on the actuator toward a first end position,a second range generating a hydraulic force in a second, oppositedirection on the actuator toward a second, opposite end, position, and aneutral range between the first and second ranges. The method comprisesduring selected conditions and when the actuator is held at the firstend position by a biasing spring, adjusting the valve to within thefirst range and closer to the neutral range than to a full actuationboundary of the first range. In one example, the variable cylinder valveactuator may include a variable cam timing system that further includesoil passages integrated into a cam journal. In another example, thehydraulically actuated variable cylinder valve actuator includes avariable cam timing vane type actuator having a biasing spring biasingthe actuator toward a retarded cam timing base position.

In this way, when operating with the variable cam timing actuator atbase timing, such as during idle conditions, the valve can be adjustedaway from the full actuation boundary of the first range, thus reducingoil leakage, such as across a cam journal. This reduced leakage can thusincrease main galley pressure and improve the performance of otherhydraulic systems in the engine. Further, such positioning of the valveis acceptable as the actuator can still be maintained at base timing. Inaddition, when it is desired to move the cam timing away from basetiming, a faster response (e.g., movement in the advance direction) canbe achieved because there is less retard pressure to overcome.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a partial engine and related systems view.

FIG. 2 shows a block diagram of an engine oil lubrication system.

FIGS. 3A and 3B show an example VCT phaser and hydraulic system.

FIG. 4 shows a high level flow chart for sending a VCT phaser commandunder selected conditions, to reduce phaser leakage and improve phaserresponse time, according to the present disclosure.

FIGS. 5-6 depict prophetic example data illustrating the neutral (null)holding position of the actuator and increased pressure achieved in oneexample.

DETAILED DESCRIPTION

The following description relates to systems and methods for controllingan engine of a vehicle, the engine having a variable cylinder valvesystem, such as a variable cam timing (VCT). For example, the engine(such as the one illustrated in FIG. 1) may include a VCT phaser toadjust the cam timing (such as, an amount of cam retard or cam advance),where the phaser is included in a hydraulic system (such as described inFIG. 2). Further, the engine may include a corresponding hydrauliccontrol system having a spool valve, as illustrated in FIGS. 3A and 3B.The hydraulic system and thus cam timing may be adjusted using a controlalgorithm, such as shown in FIG. 4, to reduce oil leakage and/orincrease oil pressure during engine operation with the cam phaser in abase position. In one particular example, the routine includes adjustingthe spool valve to a range away from a neutral/null position of thespool valve, such as illustrated in FIG. 5, during engine idlingconditions when the cam timing is commanded to be at base timing. Inthis way, it is possible to reduce oil pressure across a cam journalwhile maintaining the cam timing in the base position, thus reducing oilleakage and/or increasing oil pressure, as shown by the prophetic testresults of FIG. 6.

FIG. 1 depicts an example embodiment of a combustion chamber or cylinderof internal combustion engine 10. FIG. 1 shows that engine 10 mayreceive control parameters from a control system including controller12, as well as input from a vehicle operator 190 via an input device192. In this example, input device 192 includes an accelerator pedal anda pedal position sensor 194 for generating a proportional pedal positionsignal PP.

Cylinder (herein also “combustion chamber”) 30 of engine 10 may includecombustion chamber walls 32 with piston 36 positioned therein. Piston 36may be coupled to crankshaft 40 so that reciprocating motion of thepiston is translated into rotational motion of the crankshaft.Crankshaft 40 may be coupled to at least one drive wheel of thepassenger vehicle via a transmission system. Further, a starter motormay be coupled to crankshaft 40 via a flywheel to enable a startingoperation of engine 10. Crankshaft 40 is coupled to oil pump 208 topressurize the engine oil lubrication system 200 (the coupling ofcrankshaft 40 to oil pump 208 is not shown). Housing 136 ishydraulically coupled to crankshaft 40 via a timing chain or belt (notshown).

Cylinder 30 can receive intake air via intake manifold or air passages44. Intake air passage 44 can communicate with other cylinders of engine10 in addition to cylinder 30. In some embodiments, one or more of theintake passages may include a boosting device such as a turbocharger ora supercharger. A throttle system including a throttle plate 62 may beprovided along an intake passage of the engine for varying the flow rateand/or pressure of intake air provided to the engine cylinders. In thisparticular example, throttle plate 62 is coupled to electric motor 94 sothat the position of elliptical throttle plate 62 is controlled bycontroller 12 via electric motor 94. This configuration may be referredto as electronic throttle control (ETC), which can also be utilizedduring idle speed control.

Combustion chamber 30 is shown communicating with intake manifold 44 andexhaust manifold 48 via respective intake valves 52 a and 52 b (notshown), and exhaust valves 54 a and 54 b (not shown). Thus, while fourvalves per cylinder may be used, in another example, a single intake andsingle exhaust valve per cylinder may also be used. In still anotherexample, two intake valves and one exhaust valve per cylinder may beused.

Exhaust manifold 48 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 30. Exhaust gas sensor 76 is showncoupled to exhaust manifold 48 upstream of catalytic converter 70 (wheresensor 76 can correspond to various different sensors). For example,sensor 76 may be any of many known sensors for providing an indicationof exhaust gas air/fuel ratio such as a linear oxygen sensor, a UEGO, atwo-state oxygen sensor, an EGO, a HEGO, or an HC or CO sensor. Emissioncontrol device 72 is shown positioned downstream of catalytic converter70. Emission control device 72 may be a three-way catalyst, a NOx trap,various other emission control devices or combinations thereof.

In some embodiments, each cylinder of engine 10 may include a spark plug92 for initiating combustion. Ignition system 88 can provide an ignitionspark to combustion chamber 30 via spark plug 92 in response to sparkadvance signal SA from controller 12, under select operating modes.However, in some embodiments, spark plug 92 may be omitted, such aswhere engine 10 may initiate combustion by auto-ignition or by injectionof fuel, as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, fuel injector 66A is shown coupled directly to cylinder 30 forinjecting fuel directly therein in proportion to the pulse width ofsignal dfpw received from controller 12 via electronic driver 68. Inthis manner, fuel injector 66A provides what is known as directinjection (hereafter also referred to as “DI”) of fuel into cylinder 30.

Controller 12 is shown as a microcomputer, including microprocessor unit102, input/output ports 104, an electronic storage medium for executableprograms and calibration values shown as read only memory chip 106 inthis particular example, random access memory 108, keep alive memory110, and a conventional data bus. Controller 12 is shown receivingvarious signals from sensors coupled to engine 10, in addition to thosesignals previously discussed, including measurement of inducted mass airflow (MAF) from mass air flow sensor 100 coupled to throttle 20; enginecoolant temperature (ECT) from temperature sensor 112 coupled to coolingsleeve 114; a profile ignition pickup signal (PIP) from Hall effectsensor 118 coupled to crankshaft 40; and throttle position TP fromthrottle position sensor 20; absolute Manifold Pressure Signal MAP fromsensor 122; an indication of knock from knock sensor 182; and anindication of absolute or relative ambient humidity from sensor 180.Engine speed signal RPM is generated by controller 12 from signal PIP ina conventional manner and manifold pressure signal MAP from a manifoldpressure sensor provides an indication of vacuum, or pressure, in theintake manifold. During stoichiometric operation, this sensor can givean indication of engine load. Further, this sensor, along with enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In one example, sensor 118, which is also used as anengine speed sensor, produces a predetermined number of equally spacedpulses every revolution of the crankshaft.

In this particular example, temperature T_(cat1) of catalytic converter70 is provided by temperature sensor 124 and temperature T_(cat2) ofemission control device 72 is provided by temperature sensor 126. In analternate embodiment, temperature Tcat1 and temperature Tcat2 may beinferred from engine operation.

Continuing with FIG. 1, a variable camshaft timing (VCT) system 19 isshown. In this example, an overhead cam system is illustrated, althoughother approaches may be used Specifically, camshaft 130 of engine 10 isshown communicating with rocker arms 132 and 134 for actuating intakevalves 52 a, 52 b and exhaust valves 54 a, 54 b. VCT system 19 may beoil-pressure actuated (OPA), cam-torque actuated (CTA), or a combinationthereof. By adjusting a plurality of hydraulic valves to thereby directa hydraulic fluid, such as engine oil, into the cavity (such as anadvance chamber or a retard chamber) of a camshaft phaser, valve timingmay be changed, that is advanced or retarded. As further elaboratedherein, the operation of the hydraulic control valves may be controlledby respective control solenoids. Specifically, an engine controller maytransmit a signal to the solenoids to move a valve spool that regulatesthe flow of oil through the phaser cavity. As used herein, advance andretard of cam timing refer to relative cam timings, in that a fullyadvanced position may still provide a retarded intake valve opening withregard to top dead center, as just an example.

Camshaft 130 is hydraulically coupled to housing 136. Housing 136 formsa toothed wheel having a plurality of teeth 138. In the exampleembodiment, housing 136 is mechanically coupled to crankshaft 40 via atiming chain or belt (not shown). Therefore, housing 136 and camshaft130 rotate at a speed substantially equivalent to each other andsynchronous to the crankshaft. In an alternate embodiment, as in a fourstroke engine, for example, housing 136 and crankshaft 40 may bemechanically coupled to camshaft 130 such that housing 136 andcrankshaft 40 may synchronously rotate at a speed different thancamshaft 130 (e.g. a 2:1 ratio, where the crankshaft rotates at twicethe speed of the camshaft). In the alternate embodiment, teeth 138 maybe mechanically coupled to camshaft 130. By manipulation of thehydraulic coupling as described herein, the relative position ofcamshaft 130 to crankshaft 40 can be varied by hydraulic pressures inretard chamber 142 and advance chamber 144 (not shown in FIG. 3, butshown in FIG. 1). By allowing high pressure hydraulic fluid to enterretard chamber 142, the relative relationship between camshaft 130 andcrankshaft 40 is retarded. Thus, intake valves 52 a, 52 b and exhaustvalves 54 a, 54 b open and close at a time earlier than normal relativeto crankshaft 40. Similarly, by allowing high pressure hydraulic fluidto enter advance chamber 144, the relative relationship between camshaft130 and crankshaft 40 is advanced. Thus, intake valves 52 a, 52 b, andexhaust valves 54 a, 54 b open and close at a time later than normalrelative to crankshaft 40.

While this example shows a system in which the intake and exhaust valvetiming are controlled concurrently, variable intake cam timing, variableexhaust cam timing, dual independent variable cam timing, dual equalvariable cam timing, or other variable cam timing may be used. Further,variable valve lift may also be used. Further, camshaft profileswitching may be used to provide different cam profiles under differentoperating conditions. Further still, the valvetrain may be roller fingerfollower, direct acting mechanical bucket, electrohydraulic, or otheralternatives to rocker arms.

Continuing with the variable cam timing system, teeth 138, rotatingsynchronously with camshaft 130, allow for measurement of relative camposition via cam timing sensor 150 providing signal VCT to controller12. Teeth 1, 2, 3, and 4 may be used for measurement of cam timing andare equally spaced (for example, in a V-8 dual bank engine, spaced 90degrees apart from one another) while tooth 5 may be used for cylinderidentification. In addition, controller 12 sends control signals (LACT,RACT) to conventional solenoid valves (not shown) to control the flow ofhydraulic fluid either into retard chamber 142, advance chamber 144, orneither.

Relative cam timing can be measured in a variety of ways. In generalterms, the time, or rotation angle, between the rising edge of the PIPsignal and receiving a signal from one of the plurality of teeth 138 onhousing 136 gives a measure of the relative cam timing. For theparticular example of a V-8 engine, with two cylinder banks and afive-toothed wheel, a measure of cam timing for a particular bank isreceived four times per revolution, with the extra signal used forcylinder identification.

As described above, FIG. 1 merely shows one cylinder of a multi-cylinderengine, and that each cylinder has its own set of intake/exhaust valves,fuel injectors, spark plugs, etc.

FIG. 2 shows an example embodiment of an engine oil lubrication system200 with an oil pump 208 coupled to crankshaft 40 (not shown), andincluding various oil subsystems 216, 218, 220. The oil subsystem mayutilize oil flow to perform some function, such as lubrication,actuation of an actuator, etc. For example, one or more of the oilsubsystems 216, 218, 220 may be hydraulic systems with hydraulicactuators and hydraulic control valves. Further, the oil subsystems 216,218, 220 may be lubrication systems, such as passageways for deliveringoil to moving components, such as the camshafts, cylinder valves, etc.Still further non-limiting examples of oil subsystems are camshaftphasers, cylinder walls, miscellaneous bearings, etc.

Oil is supplied to the oil subsystem through a supply channel and oil isreturned through a return channel. In some embodiments, there may befewer or more oil subsystems.

Continuing with FIG. 2, the oil pump 208, in association with therotation of crankshaft 40 (not shown), sucks oil from oil reservoir 204,stored in oil pan 202, through supply channel 206. Oil is delivered fromoil pump 208 with pressure through supply channel 210 and oil filter 212to main galley 214. The pressure within the main galley 214 is afunction of the force produced by oil pump 208 and the flow of oilentering each oil subsystem 216, 218, 220 through supply channels 214 a,214 b, 214 c, respectively. Oil returns to oil reservoir 204 atatmospheric pressure through return channel 222. Oil pressure sensor 224measures main galley oil pressure and sends the pressure data tocontroller 12 (not shown).

The level of the main galley oil pressure can affect the performance ofone or more of the oil subsystems 216, 218, 220, for example the forcegenerated by a hydraulic actuator is directly proportional to the oilpressure in the main galley. When oil pressure is high, the actuator maybe more responsive; when oil pressure is low, the actuator may be lessresponsive. Low oil pressure may also limit the effectiveness of engineoil to lubricate moving components. For example, if the main galley oilpressure is below a threshold pressure, a reduced flow of lubricatingoil may be delivered, and component degradation may occur.

Additionally, the main galley oil pressure is highest when there is noor reduced flow of oil out of the main galley. Thus, leakage ofhydraulic actuators in the oil subsystems can reduce main galley oilpressure. Further, one particular source of oil leakage can occur in thevariable cam timing phaser, as described in further detail with regardto FIGS. 3A-3B.

FIGS. 3A and 3B show an oil subsystem 220 in two different states. Oilsubsystem 220 (herein also “phaser”) is comprised of variable cam timingactuator (herein also “actuator”) 360, variable force solenoid (hereinalso “solenoid”) 310, oil control spool valve (herein also “spoolvalve”) 300, cam journal 370, and hydraulic channels (herein also“channels”) 316, 317, 318, 320, 322. Channel 316 connects main galley214 to spool valve 300; channels 317, 318 connect spool valve 300 toreturn channel 222; channel 320 connects spool valve 300 to retardchamber 142 in actuator 360 via cam journal passage 342; channel 322connects spool valve 300 to advance chamber 144 in actuator 360 via camjournal passage 344. Cam journal 370 includes cam shaft 130, cam journalpassages 342 and 344, cam journal cap 380, and cylinder head cam bore381. Cam journal cap 380, mechanically coupled to the cylinder head (notshown), forms a cylindrical bearing within which cam shaft 130 mayrotate. In FIG. 3A, a cut-away view of cam journal cap 380 is shown withcap top 380 a, cylinder head cam bore 381, and cap seal landing 380 c.Oil passages may be integrated into cam journal cap 380 as shown oneither side of cap seal landing 380 c. Cam journal passage 342 providesa hydraulic channel for oil between channel 320 and retard chamber 142.Cam journal passage 344 provides a hydraulic channel for oil betweenchannel 322 and advance chamber 144. Cap seal landing 380 c providesseparation between cam journal passages 342 and 344. Thus, in oneparticular example, a cam-fed oil pressure actuated system may be used.

Actuator 360 is comprised of rotor 330, housing 136, retard chamber 142,advance chamber 144 (not shown), locking pin 332, and optional returnspring 334. Rotor 330 is attached to camshaft 130 so it rotates at thesame speed as camshaft 130. Rotor 330 is hydraulically coupled tohousing 136. Phaser vanes 330 a, 330 b, 330 c, 330 d move within therecesses formed by retard chamber 142 and advance chamber 144. Spoolvalve 300 allows rotor 330 to move, by permitting oil flow into retardchamber 142 and out of advance chamber 144 or vice versa, depending onthe desired direction of movement (that is, depending on whether a camadvance or a cam retard is desired). During a cam retard, oil fromsupply channel 316 flows through spool valve 300 and channel 320 and camjournal passage 342 into retard chamber 142 while oil is pushed fromadvance chamber 144 into cam journal passage 344 and channel 322 throughspool valve 300 and out channel 318. During a cam advance, oil fromsupply channel 316 flows through spool valve 300 and channel 322 and camjournal passage 344 into advance chamber 144 while oil is pushed fromretard chamber 142 into cam journal passage 342 and channel 320 throughspool valve 300 and out channel 317. Housing 136 forms a mechanical stopfor rotor 330. When retard chamber 142 is maximally open and rotor 330is resting against housing 136, actuator 360 is at the retard endposition (herein also “base position”) and cam timing is maximallyretarded. When advance chamber 144 is maximally open and rotor 330 isresting against housing 136, actuator 360 is at the advance end positionand cam timing is maximally advanced. Optional return spring 334 andlocking pin 332 may hold rotor 330 in the base position when oilpressure is low, such as during cold start. As oil pressure increases,locking pin 332 can be retracted so rotor 330 is free to move asdescribed previously. When return spring 334 is present, return spring334 generates a force that biases rotor 330 toward the base positionregardless of oil pressure.

Spool valve 300 is comprised of a sleeve 308 for receiving a spool 314with spool lands 314 a, 314 b, 314 c and a biasing spring 312. Solenoid310, controlled by electronic control unit (ECU) 302 (which may becontroller 12), moves spool 314 within sleeve 308. The position of spool314 is determined by balancing the force of biasing spring 312 againstthe force generated by solenoid 310. Spool landings 314 a, 314 b, 314 care used to restrict or block the flow of oil through the hydraulicchannels. Spool 314 can be adjustable such that spool valve 300 operatesamong a plurality of ranges including a first range generating ahydraulic force in a first direction on the actuator toward a first endposition, a second range generating a hydraulic force in a second,opposite direction on the actuator toward a second, opposite end,position, and a neutral range between the first and second ranges. Inone example, the first range is a retard range, and the second range isan advancing range.

In the retarding range, oil flows from spool valve 300 into retardchamber 142 forcing actuator 360 to retard cam timing, up to themaximally retarded cam timing. Spool landing 314 a blocks channel 317, achannel is open from channel 316 to channel 320 between spool landings314 a, 314 b, and a channel is open from channel 322 to channel 318between spool landings 314 b, 314 c. One case of the retarding range iswhen solenoid 310 is not energized (e.g. has no current applied to it)and actuator 360 is at the base position. In the advancing range, oilflows from spool valve 300 into advance chamber 144 forcing actuator 360to overcome return spring 334 and advance cam timing, up to themaximally advanced cam timing. Spool landing 314 c blocks channel 318, achannel is open from channel 316 to channel 322 between spool landings314 b, 314 c, and a channel is open from channel 320 to channel 317between spool landings 314 a, 314 b in the advancing range. In theneutral range, hydraulic forces on the actuator are substantiallybalanced so actuator 360 will neither advance nor retard cam timing.Torque from return spring 334 is countered by a positive pressuredifferential from advance chamber 144 to retard chamber 142. In theneutral range, spool landing 314 c blocks channel 318, a weak channel isopen from channel 316 to channel 322 between spool landings 314 b, 314c, and a weak channel is open from channel 320 to channel 317 betweenspool landings 314 a, 314 b.

As noted above, FIGS. 3A-3B show spool valve 300 in two differentpositions, one generating more leakage through cam journal 370, theother generating less leakage through cam journal 370. FIG. 3A shows asubstantially de-energized setting for solenoid 310 when actuator 360 isto be held in the base position, and timing is to be held at basetiming. Solenoid 310 is de-energized so high pressure oil from maingalley 214 can flow through hydraulic channels 316, 320, and 342 intoretard chamber 142 and atmospheric pressure oil can flow from advancechamber 144 to oil reservoir 204 through hydraulic channels 344, 322,and 318. The pressure difference creates torque 336 that pushes againstthe vanes of rotor 330 to hold actuator 360 in the base position. Returnspring 334 also creates torque holding actuator 360 in the baseposition. Pressure in hydraulic channels 316, 322, and 342 leading toretard chamber 142 is near the main galley pressure and pressure inhydraulic channels 318, 322, and 344 leading from advance chamber 144 isnear atmospheric pressure. The high pressure difference may create highleakage through cam journal 370 as high pressure oil leaks through thesmall radial clearance between cam shaft 130 and cap seal landing 380 cfrom cam journal passage 342 to cam journal passage 344. From camjournal passage 344, the oil flows through channels 322 and 318 to oilreservoir 204. Cam journal leakage can reduce the main galley pressurewhich can affect the performance of other oil subsystems, as noted inFIG. 2. The pressure difference also increases the delay when firstadvancing from base timing. Oil subsystem 220 flows enough oil toreverse the pressure differential in the phaser and to generate pressurein the advance direction to overcome return spring 334 before the camtiming can begin to advance.

During selected conditions, such as during engine idle when the engineoil exceeds a threshold temperature and when the engine oil pressureexceeds a threshold pressure, it is possible to maintain base timingwhile also reducing cam journal oil leakage. FIG. 3B shows phaser 220under such conditions such that actuator 360 is in the base position andspool valve 300 is in the retarding range, but at an end of theretarding range near the neutral range. ECU 302 applies current tosolenoid 310 such that spool 314 is moved until the hydraulic path fromchannel 316 to channel 320 is slightly open and the hydraulic path fromadvance chamber 144 through channels 344, 322, 318 is slightly open.Pressure in retard chamber 142 is sufficient to maintain actuator 360 inthe base position, but the pressure in retard chamber 142 and hydraulicchannels 342 and 320 is considerably lower than the high pressure frommain galley 214. Pressure in advance chamber 144 and hydraulic channels344 and 322 is near the atmospheric pressure of oil reservoir 204. Oilleakage across cap seal landing 380 c from cam journal passage 342 tocam journal passage 344 is reduced because the pressure differenceacross cam journal passage 342 and cam journal passage 344 is much lessthan when solenoid 310 is de-energized. Rotor 330 is held in place byforces from return spring 334 and the pressure in retard chamber 142 sothat base timing can be maintained. The reduced oil pressure will resultin faster response time, as compared to the oil subsystem in FIG. 3A,when cam timing begins to advance. The smaller initial pressure inretard chamber 142 requires less oil to flow to generate enough pressurein the advance direction to overcome return spring 334. As such, in theparticular example of a cam-fed oil pressure actuated system, it ispossible to address oil leakage that may occur between the advance andretard oil passages in the cam journal bearing due to the pressuredifferential between the two passages.

As further elaborated with reference to FIG. 4, a routine 400 may beexecuted by an engine controller, such as 12, to carry out a controlmethod for a hydraulically actuated variable cylinder valve actuatorcoupled to a cylinder valve of the engine, such as the variable camtiming actuator 360, controlled by a hydraulic valve, such as spoolvalve 300. In one example, the method includes, during selectedconditions and when the actuator is held at a first end position by thebiasing spring, adjusting the hydraulic valve to within a first rangeand closer to the neutral range than to a full actuation boundary of thefirst range. For example, the actuator may be held in the retard rangenear the neutral range, thus reducing oil pressure across the actuatorthereby reducing oil leakage and enabling a faster response when movingthe actuator away from the first end position. Further, differentoperating modes may be carried out depending on operating conditions.For example, in a first mode during selected conditions and when thevariable cam timing actuator is held at the fully retarded timingposition by the biasing spring, the routine may include adjusting thevalve to within a first retarded range and closer to the neutral range.In a second mode, the routine may include advancing the cam timing fromthe fully retarded timing position by adjusting the spool valve fromwithin the first retarded range and closer to the neutral range to thesecond advance range.

Therefore, returning to routine 400, at 402, the method includesmeasuring and/or estimating the engine operating conditions. Theconditions assessed may include measured VCT timing, commanded VCTtiming, engine oil temperature, engine speed, idle speed, barometricpressure, a driver-demanded torque (for example, from a pedal-positionsensor), manifold pressure (MAP), manifold air flow (MAF), airtemperature, vehicle speed, etc. An idle flag can be set when the enginespeed is equal to or below the idle speed for the current engineoperating conditions. The idle flag will be clear if the engine speedexceeds the idle speed.

A determination is made at 404 whether the idle flag has been set. Ifthe idle flag is not set then the routine is ended. If the idle flag isset, at 406, it is determined whether conditions for a potential oilleak are present. As non-limiting examples, oil leaks are more likelywhen the engine oil exceeds some threshold temperature, when the engineoil pressure exceeds some threshold pressure, when vehicle speed is zeroand when a driver pedal depression is less than a threshold amount andwhen wheel brakes are actuated, and when engine speed is controlled to adesired idle speed, etc. If conditions for oil leakage are not present,the routine ends. In general, routine 400 may be used at a hightemperature (e.g., above a threshold temperature) and/or below a lowspeed threshold so as not to degrade full economy across the entire oiltemperature range.

If conditions for oil leakage exist, a determination is made at 408whether active VCT control in enabled or disabled. Active VCT controluses feedback to calibrate solenoid current as engine operatingconditions change over time. Active VCT control may be disabled when itis prudent to minimize the potential for introducing disturbances toengine combustion, such as during idle, during cold start and warm upfrom ambient conditions. Active VCT control may also be disabled whenthe cam timing is fully advanced or fully retarded. Active VCT controlmay transition from disabled to enabled when cam timing is neither fullyadvanced nor fully retarded and the spool valve is in the null position.Routine 400 proceeds from 408 to 418 when active VCT control is enabled.Routine 400 proceeds from 408 to 410 when active VCT control isdisabled.

At 418, active feedback control of cam timing can be performed. Duringactive feedback control, the measured relative cam timing is used in afeedback control loop to adjust advance or retard pressure (e.g., viaspool valve 300). Next, at 420, the holding current for maintainingspool valve 300 in the null position can be observed and stored in atable indexed by various parameters such as engine oil temperature,engine speed, etc. The null position can be determined when actuator 360is not fully advanced or fully retarded and the measured cam timing isnot currently changing. From the null position, increasing solenoidcurrent to the point where actuator 360 starts to advance will give therightmost null position. From the null position, decreasing solenoidcurrent to the point where actuator 360 starts to retard will give theleftmost null position. As one example, the observing may includedetermining limits (leftmost and rightmost null positions) of theneutral range while performing feedback control when the actuator isaway from and between the first end position and the second endposition. The storing may include adjusting the leftmost and rightmostnull positions in a table indexed by the current engine operatingconditions. Further, once the neutral range is learned, the first(retard) range limits and the second (advance) range limits can bedetermined and table entries corresponding to current engine operatingconditions can be adjusted in response to the determined neutral range.

A determination is made at 410 whether the measured cam timing is atbase timing. If the measured cam timing is not at base timing, at 416,timing degradation may be indicated and the routine can end. If themeasured cam timing is at base timing, at 412, the learned null positionfor the current operating conditions can be retrieved. At 414, solenoidcurrent can be driven with the value below null but still in theretarding direction so actuator 360 is held in the base position,leakage is reduced between cam journal passages 342 and 344, and maingalley pressure is increased.

In one particular example, at 414, solenoid current adjusts the spoolvalve to within the first range and closer to the neutral range than toa full actuation boundary of the first range, where the first range maybe the retarding range and the second range may be the advancing range.One example of near the neutral range could be adjusting the spool valveto be within 20% of the neutral range. Another example of near theneutral range could be adjusting the spool valve so that oil flow in theretard direction is less than 40% of maximum retard flow. 414 mayinclude adjusting spool valve 300 to at least partially blockcommunication to an actuator chamber (e.g., the retard chamber 142),that generates a torque toward the spring-generated base position.

In addition to reduced leakage, energizing solenoid 310 has the addedadvantage of improving the response time of the phaser when it movesfrom the base position to a more advanced position. Since the pressuredifferential is reduced between retard passage 342 and advance passage344 the system may respond faster in the advance direction as less oilflow may be needed to generate the pressure differential to begin movingrotor 330.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be encoded as microprocessor instructionsand stored into the computer readable storage medium in the enginecontrol system.

FIG. 5 shows a prophetic example of two characterizations of solenoidcurrent versus oil flow through the oil control valve spool. One curveshows oil flow as current is swept from 0 amps to 1 amp and the othercurve shows oil flow as current is swept from 1 amp to 0 amps. Thedifferent curves show hysteresis in the oil flow versus current.Retarding range 510, neutral range 520, and advancing range 530 areillustrated. The leftmost end 560 (full retarding actuation boundary) ofthe retarding range is where the solenoid is de-energized and where theactuator will be forced to the first end position. The leftmost nullposition 570 is also the rightmost end of the retarding range. Theleftmost null position 570 is where forces in the advance and retarddirections are balanced such that cam timing will be neither advancingnor retarding, but slight additional retard pressure will cause camtiming to retard. The rightmost null position 580 is also the leftmostend of the advancing range. The rightmost null position 580 is whereforces in the advance and retard directions are balanced such that camtiming will be neither advancing nor retarding, but slight additionalretard pressure will cause cam timing to retard. The null position maybe the average of the leftmost null position and rightmost nullposition. The rightmost end 590 (full advancing actuation boundary) ofthe advancing range is where the solenoid is fully energized and wherethe actuator will be forced to the second end position. Operatingcondition 540 shows leakage through cam journal 370 when actuator 360 isat the base position and solenoid 310 is de-energized, as in FIG. 3A,for example. Operating condition 550 shows leakage through cam journal370 when solenoid current is in the first range, but near neutral range520, as in FIG. 3A, for example. In one example, the routine of FIG. 4may select range 550 as a desired set-point for the spool valve in 412and 414.

FIG. 6 shows a prophetic example of the characterization of solenoidcurrent versus main galley oil pressure. Main galley pressure 610 occurswhen solenoid 310 is de-energized. Main galley pressure 620 peaks whensolenoid 310 is operating in or near the neutral range 520. Main galleypressure 630 occurs when solenoid 310 is fully energized.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, gasoline, diesel and other engine types andfuel types. The subject matter of the present disclosure includes allnovel and nonobvious combinations and subcombinations of the varioussystems and configurations, and other features, functions, and/orproperties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application.

Such claims, whether broader, narrower, equal, or different in scope tothe original claims, also are regarded as included within the subjectmatter of the present disclosure.

The invention claimed is:
 1. A method of controlling an engine includinga hydraulically actuated cylinder valve actuator controlled by ahydraulic valve adjustable among a plurality of ranges including a firstrange generating hydraulic force in a first direction on the actuatortoward a first end position, a second range generating hydraulic forcein a second, opposite direction on the actuator toward a second,opposite end, position, and a neutral range between the first and secondranges, comprising: when the actuator is at the first end position,adjusting the hydraulic valve to within the first range and closer tothe neutral range than to a full actuation boundary of the first range.2. The method of claim 1 wherein the adjusting the hydraulic valveincludes adjusting the hydraulic valve to near the neutral range, andwhere hydraulic forces on the actuator are substantially balanced in theneutral range.
 3. The method of claim 1 wherein the hydraulic valve is aspool valve, and wherein the adjusting includes adjusting the spoolvalve to at least partially block communication to a drain in the spoolvalve and an actuator chamber.
 4. The method of claim 1 furthercomprising determining limits of the neutral range while performingfeedback control when the actuator is away from and between the firstend position and the second end position.
 5. The method of claim 4further comprising adjusting determinations of limits of the firstand/or second ranges in response to the determined neutral range, wherewhen the actuator is held at the first end position, adjusting thehydraulic valve to within the first, adjusted, range.
 6. The method ofclaim 1 wherein the adjusting is performed during selected conditionsincluding during idle.
 7. The method of claim 6 wherein the selectedconditions include when vehicle speed is zero and when a driver pedaldepression is less than a threshold amount and when wheel brakes areactuated, and when engine speed is controlled to a desired idle speed.8. The method of claim 1 wherein the adjusting is performed duringselected conditions including when not performing feedback control ofcam timing, the feedback control including the actuator being betweenthe first and second end positions.
 9. The method of claim 8 wherein theselected conditions include when engine oil temperature is above athreshold value.
 10. The method of claim 1 wherein the actuator is avariable cam timing actuator, the method further comprising adjustingthe hydraulic valve to advance cam timing from the first end position byadjusting the hydraulic valve from within the first range and closer tothe neutral range than to a full actuation boundary of the first rangeto within the second range.
 11. A method of hydraulically controlling avariable cam timing actuator of an engine through an electromechanicallyactuated solenoid spool valve, the spool valve adjustable among aplurality of ranges including a first range generating a hydraulic forcein a retard direction on the variable cam timing actuator toward a firstretarded end position, a second range generating a hydraulic force in asecond advance direction on the variable cam timing actuator toward asecond, advanced end, position, and a neutral range between the firstand second ranges, the method comprising: during engine operation andwhen the variable cam timing actuator is maintained in a fully retardedposition, adjusting the spool valve to be within the first range closerto the neutral range than to a full retard end of the first range; andduring engine operation and when the variable cam timing actuator isaway from the fully retarded position, adjusting the spool valve basedon feedback cam timing to maintain a desired cam timing position. 12.The method of claim 11 wherein the adjusting the spool valve to bewithin the first range closer to the neutral range than to a full retardend of the first range includes adjusting the spool valve to be within20% of the neutral range.
 13. The method of claim 11 wherein theadjusting the spool valve to be within the first range closer to theneutral range than to a full retard end of the first range includesadjusting the spool valve so that oil flow in the retard direction isless than 40% of maximum retard flow.
 14. The method of claim 11 furthercomprising, during feedback adjustment, learning limits of the neutralrange.
 15. The method of claim 14 wherein the engine operation when thevariable cam timing actuator is maintained in the fully retardedposition includes during engine idling condition and when the engine iswarming up from ambient temperature.
 16. A system for an engine,comprising: a hydraulically actuated variable cam timing actuator; a camwith oil passages used to deliver oil from oil passages in a cam cap tothe variable cam timing actuator coupled to the cam; a cylinder havingat least a cylinder valve actuated by the cam; a hydraulic spool valvecoupled to the variable cam timing actuator, the spool valve adjustableamong a plurality of ranges including a first retard range generating ahydraulic force in a first direction on the variable cam timing actuatortoward a fully retarded timing position, a second advance rangegenerating a hydraulic force in a second, opposite direction on thevariable cam timing actuator toward a fully advanced timing position,and a neutral range between the first and second ranges; and computerreadable storage medium having instructions encoded therein, including:instructions for operating in a first mode during selected conditionsand when the variable cam timing actuator is held at the fully retardedtiming position, adjusting the spool valve to within the first retardrange and closer to the neutral range; and instructions for operating ina second mode that includes advancing the cam timing from the fullyretarded timing position by adjusting the spool valve from within thefirst retard range and closer to the neutral range, to the secondadvance range.
 17. The system of claim 16 wherein the selectedconditions during the first mode include during engine idling, whenvehicle speed is zero and when a driver pedal depression is less than athreshold amount, and when wheel brakes are actuated, and wherein oil issupplied through the oil passages in the cam to the hydraulicallyactuated variable cam timing actuator.
 18. The system of claim 17wherein the selected conditions during the first mode include when notperforming feedback control of cam timing, the feedback controlincluding the variable cam timing actuator being between the fullyretarded and fully advanced timing positions.
 19. The system of claim 16wherein the selected conditions during the first mode include whenengine oil temperature is above a threshold value.
 20. A method ofhydraulically controlling a VCT-actuator through a spool valvecomprising: during engine operation and when the VCT-actuator ismaintained in a fully retarded position, adjusting the spool valve to becloser to a neutral range than to the fully retarded position; andduring engine operation and when the VCT-actuator is away from the fullyretarded position, adjusting the spool valve based on feedback of camtiming to maintain a desired cam timing.